The invention relates to an electric toothbrush with an electric motor, which generates a motion of rotation and has a motor shaft, a gear that converts the motion of rotation into a reciprocating stroke, and a slip-on brush, which is to be attached to a handle segment so as not to be rotatable in said handle segment and which has a reciprocatable toothed rack in order to drive the rotatable bristle carriers.
Such an electric toothbrush is the subject matter of the U.S. Pat. No. 4,827,550 issued May 9, 1989 and which is of common ownership with the instant application. In the case of the toothbrush known in this document a contrate gear, which is driven by means of a pinion by the electric motor in the handle segment, is disposed in an eccentric, from which a crank arm leads to a reciprocatable connecting rod that leads out of the handle segment. This connecting rod couples with a toothed rack in the slip-on brush, when said brush is slid on the handle segment. The toothed rack generates in turn an alternating motion of rotation of the individual bristle carriers in the brush head.
If one wants to attain an adequately long stroke of the toothed rack, so that the bristle tufts exert more than one rotation at each stroke, the contrate gear must have a relatively large diameter. This leads to relatively great forces which subject the gear to wear. Exchanging a defect gear is either not at all possible or only possible with great difficulty because the gear must be housed inside the handle segment so as to be water-tight so that it is not accessible from the outside.
The problem on which the invention is based is to design an electric toothbrush of the aforementioned kind in such a manner that its gear may be exchanged as easily as possible in order to convert the motion of rotation of the electric motor into a reciprocating motion.